In recent years attention has focussed on quantum devices with ultrafine structures, such as quantum wires and quantum boxes, and on methods of fabricating such devices. Quantum devices are well known and are devices in which carriers (electrons and/or holes) are confined into a small part of the device in one, two and three dimensions, respectively. The dimensions of such devices are sufficiently small, in the order of 10 nm, so as to be comparable to the wavelength of electrons and holes. Thus, the electrons and holes behave not only as particles, but also as waves. Fabricating methods that have been used include those involving combinations of wet and dry etching techniques. Ion-beam technology has also been used to fabricate submicron quantum devices.
The application of selective epitaxial growth techniques for the fabrication of nanometric-scale capillary tubes and boxes has been disclosed, for example in an article in APPLIED PHYSICS LETTERS, Vol. 56, Pg. 2642 (1990), by J. A. Lebens, C. S. Tsai, K. J. Vabala and T. F. Kuech. This article describes using metal-organic vapor-phase epitaxy to grow a layer of AlGaAs on a GaAs substrate with a (100) oriented surface, and using a SiN mask layer and electron-beam lithography and etching to form tubes from 90 nm to 300 nm wide and boxes 70 nm to 300 nm in diameter. However, constraints relating to etching ratios and the size of the ion beam impose limits on the degree of submicron fabrication achievable with such techniques. This makes it difficult to fabricate quantum wires and boxes that are finer and have a good interface.